The present invention relates to improvements in paper making machines, and more particularly to improvements in press sections for paper making machines for improving the removal of water from a traveling web.
In pressing water from a traveling web in a press section, the water is expressed from the web by pressure between pressing surfaces such as the nip of a pair of press rolls and the water is expressed from the web by a pressure to cause it to travel into felts on which the web is supported. It has been heretofore appreciated that the removal of water from the web will be facilitated by lowering the viscosity of the water. Efforts have been made to improve the migration of the water from the web by heating the water or by heating the water within the web by subjecting it to heat before it enters the press nip or by blowing steam against the web to increase the water temperature. These methods of directing a flow of steam against the surface of the web increase the cost of processing because heat energy is required. Further, with the relatively high speed travel of the web in a modern paper making machine, the water either is not heated or is nonuniformly heated so that a successful increase in the ability of the water to travel from the web is not accomplished. Further, heat energy is lost with the steam escaping into the air and with air mixing with the steam in the dryer room, drafts and unequal air flow will result in an unequal effect on the heating of the water in the web.
It is an object of the present invention to provide an improved method and mechanism for a press section of a paper making machine wherein increased water removal can be accomplished.
A further object of the invention is to provide an improved method and mechanism wherein the viscosity of the water within a web is improved in a press section and the water in the web is affected uniformly with a minimum requirement for heat energy.
More particularly, the invention contemplates blanketing a surface of a web immediately on the offrunning side of a press section before the web is exposed to air and applying the web to the surface of a suction roll so that the steam is held onto and carried with the surface of the web and is drawn into the web due to the pressure differential across the web surface with the steam existing in a uniform layer on the surface of the web to the exclusion of air currents on the surface.
Other objects, advantages and features, as well as equivalent methods and structures which are intended to be covered herein, will become more apparent with the teaching of the principles of the present invention in connection with the disclosure of the preferred embodiment in the specification, claims and drawings, in which: